From b40c76d0b1e2fc356c63a01d0d6eb1abd0196a73 Mon Sep 17 00:00:00 2001
From: Aniket-Engg <aniketengg.225@gmail.com>
Date: Thu, 11 Oct 2018 16:07:39 +0530
Subject: [PATCH] approve failing test

---
 contracts/mocks/SafeERC20Helper.sol | 10 +++++++---
 test/token/ERC20/SafeERC20.test.js  |  4 ++++
 2 files changed, 11 insertions(+), 3 deletions(-)

diff --git a/contracts/mocks/SafeERC20Helper.sol b/contracts/mocks/SafeERC20Helper.sol
index 838a2512c..c020df7dc 100644
--- a/contracts/mocks/SafeERC20Helper.sol
+++ b/contracts/mocks/SafeERC20Helper.sol
@@ -64,9 +64,9 @@ contract ERC20SucceedingMock {
     return 0;
   }
 
-    function allowance(address, address) public view returns (uint256) {
-        return _allowance;
-    }
+  function allowance(address, address) public view returns (uint256) {
+    return 10;  //non-zero allowance 
+  }
 }
 
 contract SafeERC20Helper {
@@ -140,6 +140,10 @@ contract SafeERC20Helper {
     _succeeding.safeApprove(address(0), 0);
   }
 
+  function doFailingApproveByValue() public {
+    _succeeding.safeApprove(address(0), 10);
+  }
+
   function doSucceedingIncreaseAllowance() public {
     _succeeding.safeIncreaseAllowance(address(0), 0);
   }
diff --git a/test/token/ERC20/SafeERC20.test.js b/test/token/ERC20/SafeERC20.test.js
index b1308a5b7..687e6ee87 100644
--- a/test/token/ERC20/SafeERC20.test.js
+++ b/test/token/ERC20/SafeERC20.test.js
@@ -99,6 +99,10 @@ contract('SafeERC20', function () {
     });
   });
 
+  it('should throw while approving with non-zero existing allowance', async function () {
+    await shouldFail.reverting(this.helper.doFailingApproveByValue());
+  });
+
   it('should not throw on succeeding increaseAllowance', async function () {
     await this.helper.doSucceedingIncreaseAllowance();
   });